Disposable syringes for which a single use is contemplated are well known as.Iadd., .Iaddend.for example.Iadd., .Iaddend.syringes for the injection of insulin in diabetics. Nothing, however, prevents there syringes from being reused (.Iadd.re-used) .Iaddend.in a necessarily unsterile state. The result .Iadd.is .Iaddend.that .[.contamination.]. syringes.Iadd., .Iaddend.when used .Iadd.contaminated, .Iaddend.contribute to the spreading of disease such as AIDS or hepatitis.
Accordingly.Iadd., it .Iaddend.is desirable for syringes to be designed for a single use only.Iadd., .Iaddend.to inhibit their re-use and therefore the risk of using contaminated syringes.
Previously known single use syringes usually incorporate a modification of the piston of the syringe so that it is jammed in its fully inserted position adjacent the needle. These previously known devices have the disadvantage that the piston can become inadvertently jammed prior to a liquid being drawn into the cylinder of the syringe.
Described in British Patent No. 1,550,310 and French Patent No. 2,348,708 is a single use syringe. The syringe has a detachable piston which prevents re-use of the syringe. Once the piston has been moved to the minimum volume position, movement of the piston to again draw in a liquid is prohibited since the piston rod becomes detached from the piston head. This syringe suffers from the disadvantage that the piston can become detached from the piston rod.Iadd., .Iaddend.and the syringe cannot be operated to test whether the syringe has been correctly inserted. This is usually achieved by pulling back on the piston rod to draw into the syringe a small portion of blood. A similar syringe is disclosed in British Patent No. 2,015,883.Iadd.; .Iaddend.again.Iadd., .Iaddend.this particular device shows a detachable piston which suffers from the disadvantages as discussed.
French Patent No. 2,298,340 discloses a single use syringe, with the piston being provided with a frangible diaphragm. Once the piston has been moved to the minimum volume position, a bar penetrates the diaphragm.Iadd., .Iaddend.preventing re-use of the syringe. .Iadd.Disclosed in .Iaddend.British Patent No. 1,454,540 is .Iadd.a syringe .Iaddend.of a similar construction, in that the piston is provided with a means of damaging the body of the syringe.Iadd., .Iaddend.preventing its re-use. Both .[.the.]. .Iadd.of these .Iaddend.syringes suffer from the disadvantage that they do not enable operation of the syringe to test whether the needle has .[.be.]. .Iadd.been .Iaddend.correctly located.
U.S. Pat. No. 3,951,146 discloses a single use syringe which employs a ratchet mechanism to prevent withdrawal of the piston. Again.Iadd., .Iaddend.this particular type of syringe does not enable testing to determine whether the needle has been correctly located.Iadd.. The syringe of .Iaddend.British Patent No. 2,184,657 also uses a pawl to engage behind the piston to prevent re-use. It has the same disadvantages. .Iadd.Syringes of .Iaddend.U.S. Pat. Nos. 3,478,937 and 3,890,971 also employ pawls or detent members which prevent reward movement of the piston. They suffer similar disadvantages.
U.S. Pat. No. 4,233,975 discloses a single use syringe with a plunger member which engages within a socket when the piston is moved to the minimum volume position. The plunger cannot be retracted.Iadd., .Iaddend.and .Iadd.this .Iaddend.prevents re-use of the syringe.
U.S. Pat. No. 4,650,468 is similar to several of the above discussed patents since .[.it uses.]. .Iadd.its syringe has .Iaddend.a plunger or piston which is automatically locked in a position preventing re-use.
The above discussed previously known single use syringes suffer from the further disadvantage in that they require the piston to be moved to the minimum volume .[.of.]. position before any action is taken to render the syringe inoperative.
.Iadd.U.S. Pat. Nos. 4,643,723 and 4,781,683 may be of interest also. Note too, French Patent No. 2,632,190.